Technical Field
The present invention relates to a camera link reorder and, more particularly, to control of a clock signal.
Related Art
It has become common for single-lens reflex cameras or mirrorless single-lens reflex cameras to be able to record motion pictures as well as still pictures. However, recording quality of sounds achieved during recording of motion pictures is not good enough.
Accordingly, some users of the digital SLR cameras or mirrorless SLR cameras record motion pictures records motion pictures with a camera and sounds by use of sound-specific recorders. Subsequently, the users mix the motion picture data and the audio data by use of a PC, and others, thereby creating motion pictures with high quality of motion pictures and sounds.
However, in this case, a clock error between the motion picture data and the audio data attributable to a difference in internal clocks of the respective devices. For instance, provided that the camera has a clock error of +20 ppm and that the recorder has a clock error of −20 ppm, when pictures and sounds are recorded for 24 hours by use of these devices,
the camera actually records pictures for 23 hours, 59 minutes, and 58 seconds; and
the recorder actually records sounds for 24 hours, 00 minute, and 02 seconds. Thus, the amount of discrepancy becomes greater as time elapses. Accordingly, the clock signals of the respective devices must be synchronized with each other.
JP 5359797 B describes a camera system in which an imaging element for outputting a video signal is integrated into an exchangeable lens unit. The description states that a main body unit to which the lens unit is to be linked is equipped with sound input means for acquiring audio data and sync signal input means for inputting a sync signal output from the lens unit. The description also mentions that, when motion pictures are recorded, audio data are recorded in synchronism with a sync signal output from the lens unit.
JP 2001-351366 A describes generating master clock for a slave device from word clock supplied from a master device; and performing adjustment so as to cause the master clock of the slave device to match with the word clock supplied from the master device, in accordance with a trigger signal supplied from the master device.
JP 2010-165403 A describes linking a master device with a slave device by a USB cable; generating, as operation clock, audio clock to be synchronized with a specific packet included at a predetermined cycle in transmission data or received data; and synchronizing the master device with the slave device during recording.
Incidentally, when motion pictures are recorded with a camera and when sounds are recorded with an audio-specific recorder, a conceivable way is to link the camera with the recorder by way of an HDMI (Registered Trademark). Since one cable enables transmission of videos, sounds, and control signals, wiring among devices can be simplified, the recorder can also be activated in synchronism with shutter operation of the camera.
When the camera and the recorder are linked by way of the HDMI, it will be convenient so long as the clock signal of the camera and the clock signal of the recorder can be synchronized to each other by use of the HDMI link. The related-art technique does not disclose synchronization of the clock signals by use of the HDMI signal on the premise that the camera and the recorder are linked to each other by way of the HDMI.
The HDMI includes a TMDS (Transition Minimized Differential Signaling) signal, and a clock signal can be generated from the TMDS signal. Hence, it is also conceivable to use the clock signal in both the camera and the recorder. However, a problem may occur in consistency with internal clock of the recorder and consistency with specifications of an HDMI receiver.